EP 1426569 discloses such a valve operating system having overhead cams and the relative phasing of the two cams is used to adjust, amongst other things, valve event duration.
The aim of the present invention is to implement such a system in a pushrod engine (i.e. an engine in which the cams are arranged within the engine cylinder block) where movement of the cam followers is transmitted to the valves through pushrods and rockers.
The difficulty that such a valve operating system presents when using pushrods is that there is inevitably a significant clearance in the system when a valve is closed and both of its cam followers are on the base circles of their respective cams. Steps must therefore be taken to ensure that the pushrods always remain within their sockets in the cam followers and in the valve operating rockers.